Method for washing a tow

ABSTRACT

A method for washing a tow wherein the tow is passed through a confined zone and a stream of water is forced through the tow at a minimum rate at least as great as

United States Patent [191 Taylor, Jr.

[451 Feb. 12,1974

METHOD FOR WASHING A TOW Inventor: Ernest A. Taylor, Jr., Decatur, Ala.

Monsanto Company, St. Louis, Mo.

Filed: Dec. 18, 1972 Appl. No: 315,951

Related US. Application Data Continuation-impart of Ser. No. 198,780,Nov. 15, 1971, abandoned, which is a continuation-in-part of Ser. No,51,261, June 30, 1970, abandoned.

Assignee:

US. Cl. 8/ 1 37.5, 8 /l3 7 l 34/1 5 Int. Cl. D01f 7/06 Field of Search8/137, 137.5; 134/15 [5 6] References Cited UNITED STATES PATENTS2,733,121 1/1956 Griffith, Jr. et al 8/137.5 2,768,057 10/1956Friederick 8/1375 Primary Examiner-Mayer Weinblatt M95421: i ?l 1QLEiW:RQb E lfir aqelrst 5 7 ABSTRACT A method for washing a tow whereinthe tow is passed through a confined zone and a stream of water isforced through the tow at a minimum rate at least as great as x 1,000T\fWN/h (IL/p) 13 Claims, 3 Drawing Figures m :27 I9 T E I5 L is \J T fi2340 AT 23 112 1 2/ \M; M

METHOD FOR WASHING A TOW This is a continuation-in-part of applicationSer. No. 198,780, filed Nov. 15, 1971, which was a continuation-in-partof application Ser. No. 51,261, filed June 30, 1970 for Method ForWashing A Tow in the name of Ernest A. Taylor, .lr. both now abandoned.

BACKGROUND OF THE INVENTION Man-made fibers are formed by extruding aspinning solution through a spinnerette to form a tow made up of anumber of individual filaments. 1n the production of certain man-madefibers it is usually necessary that this tow be washed during some stateof the manufacture. The washing may be for the purpose of removing aspinning. solvent, applying a dye or finish, removing excess dye after adyeing operation, neutralizing the fiber or for some other purpose.Conventionally, the tow is washed by passing it through a spray or abath or by running it through an inclined cascade in a direction counterto the fiow of water in the cascade. These approaches are inefficient,so that the tow must be run through the washing zone at a very low speedor the washing zone must extend a considerable length along the towprocessing line. The former lowers the production rate while the latterrequires the use of an excessive amount of space which might be betterused for some other purpose.

Apparatus other than cascades and sprays has been used to wash tows offilaments. US. Pat. No. 3,267,704, issued to H. G. Mueller, and US. Pat.No. 3,343,383, issued to. E. A. Taylor, Jr., for example, show apparatusused for carrying out the process wherein the washing liquid iscontinually passed back and forth through the tow until the washing iscompleted. Unfortunately, the apparatus necessary to carry out thismethod is usually several feet long and quite expensive to manufacture.

it has been discovered-that confining the tow and the washing liquid toa zone having predetermined dimensional limitations and then forcing theliquid through the tow at a rate based on the dimensions of the confinedzone and the number of filaments in the tow a vastly superior washingresult is obtained. In carrying out the method of the present inventiona very simple and inexpensive apparatus may be used, with the completewashing action being carried out in an apparatus no more than five orsix inches long. With this in mind, one of the objects of this inventionis to provide a novel and improved method for washing a tow offilaments.

Another object of this invention is to provide a method for washing atow of filaments in such a manner that excess dye or solvent is rapidlyand efficiently removed from the tow.

A further object of this invention is to provide a method for washing atow of continuous filaments in such a manner that the filaments arecompletely washed within a very short contact time.

A still further object of this invention is to assure a uniform washingof a tow of filaments.

Some tow washing devices operate much more effectively when the washingfluid is boiling, the stirring effect of the ebullient fluid serving toagitate, vibrate or separate the filaments of a tow during washing.Since in this invention a very effective filament separation is producedby the interaction of the fluid with the tow,

then another object of this invention is to eliminate a high fluidtemperature as a prerequisite for effective washing.

The objects of this invention are achieved by passing tow to be washedthrough a confined zone and forcing a stream of water or other treatmentfluid through the tow at a rate in excess of a predetermined criticalminimum value, the water being maintained at a temperature within apredetermined range. The critical minimum rate at which the water ispassed to the tow must be at least as great as x= 1,000T WN/h (pt/p)where x is the water flow rate in gallons per minute, T is the thicknessof the stream of water in inches, W is the width of the confined zone ininches, h is the thickness of the confined zone in inches, N is thenumber of filaments in the tow, p. is the viscosity of the water inpounds per foot-second, and p is the density of the water in pounds percubic foot. Preferably, the water is forced through the tow at a rate atleast three times as great as the critical minimum rate.

Other objects and advantages of the invention will become apparent whenthe following detailed description is read in conjunction with theappended drawing, in which FIG. 1 is a diagrammatic longitudinalcross-sectional view of one apparatus useful for carrying out theprocess of the present invention.

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1 showingthe cross-sectional area of the confined zone in the washing apparatusthrough which the tow is passed, and

FIG. 3 is a diagrammatic view of apparatus used with the washingapparatus in carrying out the process of the present invention. I

Referring now in detail to the drawing there is shown, in a more or lessdiagrammatic manner, a tow washer l0which is useful in carrying out themethod of the present invention. The washer 10 is made up of upper andlower units 11 and 12 which are held in a spaced relationship by sideplates 13, the side plates 13 being secured to the upper and lower units11 and 12 by screws 14. The space between the upper and lower units 11and 12 forms a confined zone through which a tow 15 passes. The lowerface 18 of the upper unit 11 and the upper face 19 of the lower unit 12and the inner faces 20 of the side plates 13 define the limits of theconfined zone through which the tow 15 passes. The confined zone thushas a. width W" and a height h" and a cross section area of Wh, as bestshown in FIG. 2.

The lower unit 12 is provided with an inlet 21 through which water orsome other liquid is applied to the tow 15. The inlet 21 extends acrossthe lower unit 12 from one of the side plates 13 to the other and thus sa width. wilh li sgl .hasa thi knsss t. AL. where A is between 0.05 and10, with T usually being no greater than about 10h, h being the heightor thickness of the confined zone, so as to concentrate the flow of thewashing liquid through the tow 15 at one location. The upper unit 11 isprovided with a recess or chamber 22 which receives the water passingthrough the tow 15 from the inlet 21.

The recess 22 directs the water back through the tow at outlets 23spaced from the inlet 21 in streams having a thickness T (FIG. 1), thevalue ofT preferably being no greater than about 10h. The preferredvalue for the dimension T is within the range of 2h to h. The waterentering the inlet 21 passes through the tow l5 and is divided intosubstantially equal parts which pass back through the tow at the outlets23. The chamber 22 completely fills with water under pressure. Thispressure forces the water through the outlets 23, and the tow 15, at ahigh velocity.

It can readily be seen that the tow is confined, at the outlets 23, to across sectional area having the dimensions W and h. The fluid passingthrough the tow at this point is confined to a cross sectional areahaving the dimensions W and T, W being width and T being thickness ofthe fluid stream.

As shown in FIG. 3, the washer l0 is'mounted over a discharge pan 30.Spaced pairs of rolls 32 and 33 feed the tow 15 through the washer at auniform speed. A pump 34 connected to the pan 30 and the inlet 21 of thewasher 10 pumps the water from the pan 30 through the washer via theinlet 21. The water exiting from the washer -10 falls into the pan 30and is recirculated by the pump through the washer. Fresh water may befed to the pan 30 from a supply 38, the pan 30 being provided with anoverflow line 39 to maintain a constant water level in the pan 30. Thefresh water supply rate is independent of the rate at which water iscirculated through the washer 10. Pairs of stripper bars 36 positionedin contact with the tow as shown in FIG. 3 are used to prevent the waterfrom flowing along the tow beyond the edges of the pan 30.

The water makes one pass through the tow at each of the outlets 23, fora total of two passes at the outlets. Since twice as much water passesthrough-the tow at the inlet 21 as at either of the outlet locations itmay be considered that the water makes a double pass, or two passes,through the tow 15 at the inlet 21. Thus, in the apparatus shown it maybe said that the water makes four passes through the tow 15. Thewatercan be deflected back and forth through the tow as many times asdesired but the method is so efficient that this is not necessary. Ateach point where the water passes through the tow the water should be,for maximum efficiency, flowing at a rate in excess of the minimum valuegiven by i i x 1,000T WN/h as set out above. If the water passes throughthe tow at a lower rate the washing efficiency will be greatly reduced.If a vigorous washing is not required the dimensions of the apparatus 10may be such that the critical minimum flow rate is exceeded at only oneof the out lets 23. In this case the washing will be highly effectiveonly at that outlet. Of course, a portion of the water in a washer suchas described above will not pass completely through the tow but willtravel along the interstices in the tow (i.e., between the filaments) tothe outlets 23. Since it would be very difficult to actually measure thewater flow rate inside the tow an easier way of determining whether theminimum flow rate is exceeded is desired. If the outlet dimensions areheld within the limits set out above, the flow rate into the inlet 21can be compared with the minimum critical flow rate.

to determine whether minimum critical flow rate is exacetate ceeded,without regard for actual flow rate in the tow or the fact that some ofthe water will travel along voids in the tow. Of course, since the oneinlet supplies two outlets, the fluid flow into the inlet must be atleast twice the critical minimum flow rate as determined by the aboveequation.

The table below shows values of u and p for water at varioustemperatures.

The following examples are included to show the efficiency of this towwashing process in removing solvent from wet spun acrylonitrilefilaments. Four washers (not shown) such as described above were used inseries, with the freshly spun tow entering washer A and then passingthrough washers, B. C and D in that order. Each washer formed a confinedzone 5.2 inches long and having the dimensions: T=9/16"; h= 3/16" and W=3 7 8 Each washer was provided with its own w ex r rm Wh Ehy W t LiQfQ-was circulated through the washer at a' rate in excess of the criticalminimum flow rate as determined by the equation given above.

Fresh water was supplied to washer D from its supply 38 and the overflowline 39 of washer D was connected overflow of washer C fed into washer Bfrom which the overflow fed into the pan 30 of washer A. The overflow ofwasher A was passed to a solvent recovery system (not shown). The freshwater supply rate, which is independent of the circulation rate in eachof the washers, was based on the weight of the tow passing through thewashers and was varied as shown in the following examples.

The tow was spun from a 93% acrylonitrile, 7% vinyl copolymer into aspin bath of 55% dimethylacetamide/45% water at 38 C. and was led fromthe spin bath into washer A. The tow entering washer A contained about50% dimethylacetamide. The tow was made up of 80,000 filaments, 3 denierper filament. The tow was advanced at a speed suchthat a given point onthe tow passed through the confined zone in 0.95 seconds. This may bereferred to as contact time" or dwell time."

EXAMPLE I Tow was spun at a rate of 600 pounds per hour. The valuesgiven under the headings A, B, C and D represent the amount of solventin the tow exiting from the washers-A, B, C and D, respectively.

tuted for the sodium phosphate in an amount sufficient Fresh WaterSolvent in tow by weight to provide a dye concentration of 0.5% based onthe pigx fiz weight of the water. The liquid flow rate was in excess A BC D of three times the critical minimum value and the time 125 7,44 L30045 025 5 Ofthe OW m the treatment zone was approximately 1.5 103 7,75235 M4 012 seconds. The filaments m the tow were dyed to a deep,

' uniform shade. The amount of dye on the fiber was approximately 2%,based on the weight of the fiber.

1O EXAMPLE V EXAMPLE H A number of runs were made using filaments ofdif- I V ferent chemical composition wherein the filaments Tow was spunat a rate of 735 pouhds e hour; Fresh were washed with water containinga finish for the purwater was added to the reservoir or pan 30 of washeris P of aPPlymg the fimsh to the filamentef'ber types D at varying ratesand the amount of solvent in the tow Included m these runs were Polyvmylehlondey P e after each washer was determined. The results are nylon ande W know to those Sk'lled m Shown in the following table the art. Thewashing fluid was 98% water and 2% of a conventional finish, at atemperature of 100 C. In addition to being washed, the filaments were 20stretched. W T T The confined zone had the following dimensions: W Freshwater Solvent in tow by weight {lb-371677; andT-Wlgi with an OverallSupply Rate lb length of 8". The number of filaments in each bundle A BC D 25 of filaments passing through the confined zone was such that theminimum critical flow rate varied up to 12.5 8.86 2.67 0.85 0.34approximately 0.1 gallon per minute for the different fibers. The actualflow rate through the confined zone was 1.2 gallons per minute. Thefollowing table shows 30 the conditions under which these runs weremade. Ap-

proximately 1% of the finish, based on the weight of The temperature ofthe water used for washing may the fiber, was applied to the fiber ineach washing run.

Fiber Polyvinyl Chloride Polyester Nylon Rayon Polyester Run NO. 1 2 3'4 5 6 7 s 9 10 11 12 13 14 15 Tow speed entering confined zone (Ft/min)39.5 20.0 59.0 10 40 50 60 10 40 10 40 -40 10 40 Tow speed leavingconfined zone (Ft/mint 156 78.0 235 56.8 180 205 240 52 162.5 45 180 4552 202.5 Time in coni'ned zone be up to 100 C. The preferred temperaturefor wash- This process may be used not only to remove solvent ingacrylonitrile filaments to remove solvent is within from a freshly spuntow but also may be used for other the range of C. to 70 C. washing suchas application of a dye or finish or removal of excess dye after adyeing process, etc. The EXAMPLE washing efficiency becomesunsatisfactory if the flow A freshly spun modacrylic tow was washed in aconrate through the washing zone is not maintained above fined zonehaving the following dimensions: W 3% the critical minimum value as setout above. Preferably, inches; h -"7n2 inehe s and? WT6TiHsTTh 16w theflow rate is at least three times the minimum rate bundle contained6,000 filaments of 50 denier each. d may be many times as great as theminimum rate, The fibers in the tow had the following composition: Theminimum dwell or contact time of the tow in the Acrylonitrile 60.6%,Vinylidene Chloride 23.0%, Vinyl Confined Z0116 e length of time that agiven Bromide 11.0%, Styrene 1.4%, Benzene Sulfonate point on the towrequires to pass through the fluid in 2.0% and Antimony Trioxide 2.0%.the confined zone) varies slightly with the washing Water at atemperature of 96 C. and containing 4% operation. For example, if it isdesired to wash the tow sodium phosphate was used for washing the fiber.The to apply a finish, a contact time of about 0.1 second or liquid flowrate was in excess of three times the critical o S all that is required.If the washing is done to i i value d h i of h tow i h treatremovesolvent from a freshly spun tow a contact time ment zone wasapproximately 1.5 seconds. The fila- 0 0f 5 econds or more should beused. ments in the tow were neutralized from a pH of 3.9 to at isClaimed is: a pH f g 5 The method of washing a tow of filaments,comprising EXAMPLE Iv a. advancing the tow through a confined zone, andThe modacrylic tow of Example 111 was washed in forcing a Stream ofliquid through the low in the water at 50 C. in a confined zone havingthe dimensions of Example lll. A conventional dye, known to be suitablefor the dyeing of modacrylic fibers, was substiconfined zone at a rategreater than x 1,000 T WN/h ,1/

"whereifiyifizn mans; mam gallons per minute, T

is the thickness of the stream of liquid in inches, W is the width ofthe confined zone in inches, h is the height of the confined zone ininches, N is the number of filaments in the tow, p. is the viscosity ofthe liquid in pounds per foot-second, and p is the density of the liquidin pounds per cubic foot.

2. The method of claim'] wherein the liquid is forced through the tow inthe confined zone at a rate at least three times as great as 10. Themethod of claim 2 wherein the tow is advanced through the confined zoneat a speed such that the tow is in contact with the liquid stream for atleast 0.1 seconds.

11. The method of washing a tow of filaments, comprising,

a. passing the tow through a washing zone, said zone confining the towin such a manner that the tow has a cross-sectional area having a widthW and a height h, b. forcing a stream of liquid through the tow in saidwashing zone, said stream of liquid having a width W and a thickness Tand also having a flow rate greater than 1,000T VWN/h (lL/P) where N isthe number of filaments in the tow, p. is the viscosity of the liquid inpound s per foot-second, and

p is the density of the liquid in pounds per cubic foot.

12. The method of claim 11 wherein the flow rate is at least three times'acrylic, nylon, polyester, polyvinyl chloride and rayon. =I=

2. The method of claim 1 wherein the liquid is forced through the tow inthe confined zone at a rate at least three times as great as x 1,000TSquare Root WN/h ( Mu 1 Rho )
 3. The method of claim 2 wherein theliquid makes at least four passes through the tow.
 4. The method ofclaim 2 wherein the temperature of the liquid is in the range of 30* C.to 100* C.
 5. The method of claim 2 wherein the filaments areacrylonitrile.
 6. The method of claim 2 wherein the filaments aremodacrylic.
 7. The method of claim 2 wherein the filaments arepolyester.
 8. The method of claim 2 wherein the filaments are nylon. 9.The method of claim 2 wherein the filaments are rayon.
 10. The method ofclaim 2 wherein the tow is advanced through the confined zone at a speedsuch that the tow is in contact with the liquid stream for at least 0.1seconds.
 11. The method of washing a tow of filaments, comprising, a.passing the tow through a washing zone, said zone confining the tow insuch a manner that the tow has a cross-sectional area having a width Wand a height h, b. forcing a stream of liquid through the tow in saidwashing zone, said stream of liquid having a width W and a thickness Tand also having a flow rate greater than 1,000T Square Root WN/h ( Mu /Rho ) where N is the number of filaments in the tow, Mu is the viscosityof the liquid in pounds per foot-second, and Rho is the density of theliquid in pounds per cubic foot.
 12. The method of claim 11 wherein theflow rate is at least three times 1,000T Square Root WN/h ( Mu / Rho )13. The method of claim 12 wherein the filaments are selected from thegroup consisting of acrylic, modacrylic, nylon, polyester, polyvinylchloride and rayon.